1. Field of the Invention
The present invention generally relates to signal communications, and more particularly, to an architecture and protocol for enabling signal communications between a frequency translation apparatus, which may be referred to herein as a frequency translation module (FTM), and an integrated receiver-decoder (IRD) or between a low noise block converter (LNB) and an IRD.
2. Background Information
In a satellite broadcast system, one or more satellites receive signals including audio and/or video signals from one or more earth-based transmitters. The satellite(s) amplify and rebroadcast these signals to signal receiving equipment at the dwellings of consumers via transponders that operate at specified frequencies and have prescribed bandwidths. Such a system includes an uplink transmitting portion (i.e., earth to satellite(s)), an earth-orbiting satellite receiving and transmitting portion, and a downlink portion (i.e., satellite(s) to earth).
In dwellings that receive signals from a satellite broadcast system, signal receiving equipment may be used to frequency shift portions of a frequency band or the entire broadcast spectrum of the satellite(s), and frequency stack the resultant output onto a single coaxial cable. However, as the number of satellites within a satellite broadcast system increases, and with the proliferation of high definition satellite channels, a point will be reached where the total bandwidth required to accommodate all of the satellites will exceed the transmission capability of the coaxial cable. It has become necessary for the satellite decoder industry to implement more satellite slots into their distribution systems. To provide for the increased number of satellite slot transmissions a more elaborate means for satellite configurations selection is required. Two primary methods used now used now for selecting these various configurations are the legacy LNB power supply method and the new Frequency Translation Module (FTM) method.
The legacy LNB power supply method controls satellite RF band selection by voltage level and a superimposed, 600 mvp-p, 22 kHz tone or lack of tone. Tone selection is accomplished by either a constant tone or a Pulse Width Modulated (PWM) tone. The industry standard for the PWM tone is called DiSEqC and is defined in the Eutelsat DiSEqC Bus Functional Specification. The two stage, output to voltage (13 or 18 volts) is typically used to select the polarity of incoming satellite signals and the tone selects various satellite slots in space.
The second method (FTM) is self powered, therefore, it does not require an LNB power supply, and uses a UART controlled 2.3 MHz, Frequency Shift Key (FSK) modulation scheme to communicate selection commands to the satellite configuration switch. The FTM switch is designed to select a satellite signal transponder from a host of satellite receiver antennas and translate it, in frequency, to a single transponder band. This new frequency shifted transponder band is then sent to the satellite decoder box through the connecting coaxial cable.
Present day satellite decoder systems need the ability to switch between these two communication methods and operate in either mode without being disturbed by the other system. If a satellite receiver system is capable of FTM operation, the conventional LNB power supply will be disabled such that all control and selection of the available satellite signals is done with the modulated 2.3 MHz, FTM communication channel. However, the LNB power supply has a low output impedance that distorts the 2.3 MHz of the FTM carrier when directly connected to the FTM circuit. The resulting distortion causes signal degradation and contamination of higher frequency bands with parasitic harmonics. The present invention described herein addresses this and/or other problems.